Well I know from trying to get the card to work under Ubuntu a while back there is no firmware available. The card gets recognised as a Terratec device but doesn't do anything. The patch is to treat the card as a different Terratec device for which there is firmware.

Meanwhile I have got a backend working on my PC, which the RasbPi can use, so I have a working "solution".

I've have a play in an idle moment and try the things you suggest. Thanks again.
M